Fl 



ora ot IMinois 



Introduction 



As the second edition (1950) has been out-oi-print for more than 

 two years, continued demand seems to warrant publication of a re- 

 vised third edition. Thanks largely to the activities of several botanists 

 in various parts of the state, many additional data are now at hand, 

 particularly regarding the occurrence and distribution of species. 



The preparation of a third edition of this book has aflforded oppor- 

 timity to make certain revisions. A number of rearrangements and 

 corrections have been made in the analytical keys. Many of the keys 

 have been rewritten entirely. Some species have been added, some 

 others have been deleted, and a few nomenclatural changes have been 

 made. New monographs and taxonomic revisions during the past 

 decade have necessitated revisionary treatment in some groups. The 

 main objective of this work is that of the previous editions, to afTord 

 a ready means of identification of the approximately 2400 species of 

 flowering plants and fernworts growing without cultivation in Illinois. 



The keys to species include, in addition to diagnostic characters, a 

 statement of habitat, frequency and distribution, time of flowering, 

 and some relevant synonymy, the intention having been to correlate 

 the valid name of the species with other names that may be found in 

 the older manuals. Suitable popular names have been provided for 

 many species. For rare plants, specimens are often cited by collector 

 and number or date. 



When the first edition of Flora of Illinois was published in 1945, 

 two of the standard botanical manuals of eastern United States were 

 between thirty and forty years old. Five years later when the second 

 edition appeared in 1950, these manuals were still in use, although the 

 eighth edition of Gray's Manual appeared somewhat later in the same 

 year, and H. A. Gleason's New Britton & Brown Illustrated Flora of 

 Northeastern United States and Adjacent Canada was published in 

 1952. Publication in 1955 of Vascular Plants of Illinois, with its exten- 

 sive synonymy, 1375 distributional maps, and a bibliography of several 

 thousand entries, has rendered largely unnecessary the repetition in this 

 edition of the extensive 27-page bibliography of the second edition. 

 Moreover, there is a list by R. H. Mohlenbrock (Rhodora 63: 19-24, 

 1961) comprising 51 ])ublications on the Illinois flora since 1955 by 

 more than a dozen difTerent authors. 



All species of vascular plants regarded by the writer as growing 

 spontaneously in Illinois have been included, provided there is evidence 

 that they are established and maintain themsehes year after year with- 

 out cultivation. Further study may reveal the presence of additional 

 species. With few exceptions, no species has been admitted, unle.ss 

 authentic specimens from Illinois have l)ecn examined. Known or 

 suspected hybrids often are mentioned, or keyed out when practicable, 



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